Centre NumberCandidate

Number

Candidate Name

International General Certificate of Secondary EducationUNIVERSITY OF CAMBRIDGE LOCAL EXAMINATIONS SYNDICATE

CHEMISTRYPAPER3

MAY/JUNE SESSION 2000

0620/3

1 hour 15 minutes

Candidates answer on the question paper.Additional materials:

Mathematical tables.

TIME 1 hour 15 minutes

INSTRUCTIONS TO CANDIDATES

Write your name, Centre number and candidate number in the spaces at the top of this page.

Answer all questions.

Write your answers in the spaces provided on the question paper.

INFORMATION FOR CANDIDATES

The number of marks is given in brackets [ ] at the end of each question or part question.Mathematical tables are available.

You may use a calculator.

A copy of the Periodic Table is printed on page 16.

This question paper consists of 14 printed pages and 2 blank pages.SB (KN/TC) OF05703/2@ UCLES 2000 [Turn over

FOR EXAMINER'S USE

1

2

3

4

5

TOTAL

1 Germanium is an element in Group IV. It was first isolated in Germany by C Winkler in 1886.

(a) It has a similar macromolecular structure to diamond. Predict two physical properties ofgermanium.

..........................................................................................................................................

[2]

(b) Explain why graphite, which is also a macromolecular form of carbon, has differentphysical properties to diamond and germanium.

... ... ......

... ... .[2]

(c) The electron distribution of a germanium atom is 2.8.18.4.Draw a diagram to show the arrangement of the valency electrons in the covalentcompound germanium tetrachloride.

Use 0 to represent an electron from germanium.Use x to represent an electron from chlorine. [3]

(d) Germanium forms a series of saturated compounds with hydrogen which resemble thealkanes.

(i) Predict the general molecular formula of these compounds of germanium andhydrogen.

[1]

(ii) Draw the structural formula for one of the above compounds that contains fourgermanium atoms per molecule.

[1]

3

(e) When aqueous solutions of germanium(II) chloride and of iron(III) chloride are mixed,the following reaction occurs.

GeCI2 + 2FeCI3 ~ 2FeCI2 + GeCI4or Ge2+ + 2Fe3+ ~ 2Fe2+ + Ge4+

(i) Is the germanium(II} chloride acting as an oxidising agent or reducing agent?Explain your choice using the idea of electron transfer.

., , ..........

, .[2]

(ii) Describe a test to show that an iron(III) salt had been changed into an iron(II) salt.

test ............................................................................................................................

result for iron(III)salt ,......................................................................................

result for iron(II) salt , """"""""""""""'[3]

4

2 Ammonia is made by the Haber process from nitrogen and hydrogen.

N2 + 3H2 ~ 2NH3 liH = -92 kJ/mole (reaction is exothermic)

(a) Describe how nitrogen can be obtained from the air.

........

""""" [2]

(b) Describe how hydrogen can be made from an alkane.

............

[2]

(c) The diagram below shows how the percentage of ammonia in the equilibrium mixturechanges with the conditions.

%NH3

%

NH3

pressure temperature

The y axis is the percentage of ammonia at equilibrium.

Fig. 2.1

(i) What is the effect of increasing the temperature on the percentage of ammonia inthe equilibrium mixture?

[1]

(ii) What is the effect of increasing the pressure upon the position of equilibrium. Doesit move to the the left, stay the same or move to the right?

[1]

(iii) Why does the position of equilibrium move as stated in (ii)?

...................................................................................................................................

[2]

(iv)

(d)

(ii)

5

Suggest an explanation why an increase in pressure increases the reaction rate.

.......................................................

""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" .[1]

Large amounts of ammonia are used in the manufacture of ammonium sulphate.

(i) What is the main use of this salt?

.[1]

Describe how crystals of ammonium sulphate can be made in the laboratory fromaqueous ammonia.

........................................................................

..................................................................................................................

...............................

[4]

6

e) Car engines and flue gases from power stations both release oxides of nitrogen into theair. These oxides are a cause of acid rain.

flue gases are acidic due to NO2

t

chimney

furnaceoxides of nitrogen form

Fig. 2.2

(i) Explain how these oxides are formed.

...................................................................................................................................

[2]

(ii) The emission of the oxides is decreased by mixing the flue gases with ammoniaand passing over a catalyst. Complete the balancing of the equation.

6NO2 + NH3 ~ 7N2 + H2O [1]

(iii) Suggest how the pH of the flue gases can show that just the right amount ofammonia is being used.

... ...

........

...[2]

7

3 Nantucket is an island twenty five miles off the coast of the USA. Some of the different fuelsand sources of energy that have been used on the island over the years are listed below.

woodwhale oilcoal and coal gaspetroleum productselectricity by cable from mainland

earliest

~at presentfuture

(a) Wood was the first carbon-based fuel used. Explain why the cycle of cutting down trees,burning the wood and the regrowth of the forest does not cause any long term changesin the amount of carbon dioxide in the atmosphere.

..........................................................................................................................................

,.....................................................................................................................................

[3]

(b) Whale oil contains unsaturated esters. As well as being used as a fuel, a number ofvaluable products can be made from this oil.

(i) Describe how you could show that whale oil contains compounds that havecarbon-carbon double bonds.

..........................................................................................

....................................................

.[3]

(ii) How could a soap be made from the oil?

.

.[2]

(Hi) Margarine used to be made from the oil by changing the unsaturated hydrocarbonchains into saturated hydrocarbon chains. Complete the word equation for thisreaction.

unsaturated + ---7 saturated

hydrocarbon hydrocarbon [1]

(c) Coal gas was made on the island by heating coal. It is a mixture of hydrogen, methane,. carbon monoxide, nitrogen etc. Explain how the percentage of hydrogen in the mixture

is increased by diffusion through a porous barrier.

.........................

......

.[3]

8

(d) A typical electricity cable would have a copper core surrounded by a polymer as anouter casing.

cross-section of an

electricity cable

outer case

of a polymer

central core

of copper

Fig. 3.1

(i) Give two reasons why the core is made from copper.

.

[2]

(ii) Give two reasons why a polymer might be a suitable material for the outer casing.

.

[2]

9

4 (a) Copper is refined by electrolysis.

anode

(i)

cathode

e

- - --- --

- -----

electrolyteaqueous copper(II) sulphateremains unchanged

- ---- --

- - --

copper electrodesmass changes

Fig. 4.1

Explain with equations why the electrodes change in mass and why the concentration ofaqueous copper(II) sulphate remains unchanged.

..........................................................................................................................................

.............

..........................................................................................................................................

[4]

(b) An alloy contains contains zinc and copper. A small sample of this alloy was dissolved in I

acid to give a solution containing zinc and copper ions. Explain what would happenIwhen an excess of each of the following reagents is separately added to this solution.

(i) iron filings

... ...

[2]

(Ji) sodium hydroxide

.. ......

.[2]

10

(c) The following diagram shows a simple cell.

voltmeter

ironelectrode

magnesiumelectrode

------

electrolytedilute sulphuric

acid-----

Fig. 4.2

(i) What is a celf?

................

.[2]

(ii) Mark on the diagram the direction of the electron flow. [1]

11

(d) A sample of impure copper was dissolved in nitric acid. The solution of copper(II) nitratewas filtered to remove solid impurities and evaporated to dryness. The solid nitrate washeated to constant mass to leave only copper(II) oxide.

ResultsMass of impure copperMass of copper oxide

=4.21 g=4.80 g

2Cu(NO3)2(S) ? 2CuO(s) + 4N02(g) + °2(g)

(i) Complete the following to determine the percentage purity of the sample of copper.

The mass of one mole of CuO = 80 g

number of moles of CuO formed - ...................... [1]

[1]mass of copper in copper(II) oxide = ......................

percentage of copper .. [1]

(ii) Calculate the total volume of gas formed at r.t.p.

total number of moles of gas formed = ..................... [2]

[1]volume of gas formed = dm3

12

5 (a) The structure of the synthetic polymer Terylene is given below.

0 0II II

-c-VJ at-c- 0-1

0 0II II

t-°-C~ A-C-O

Fig. 5.1

(i) Name the type of linkage in this polymer.

[1]

(ii) What naturally occurring substance contains the same linkage?

.[1]

(b) Another synthetic polymer is nylon. Draw the structure of a nylon.

[3]

(c) Complex carbohydrates such as starch are natural polymers.

(i) Name the three elements present in carbohydrates.

.. .[1]

(ii) Draw the structure of a complex carbohydrate.

[2]

13

(d) Chromatography is used to identify simple carbohydrates, such as sugars, in plantmaterial.

solvent front

chromatographypaper

fructose.

sucrose.glucose. datumline

----- - - - - levelof solvent

original positionsof samples of sugar

Fig. 5.2)

A leaf is ground with 50% aqueous alcohol to give a colourless solution of the sugars.This solution is concentrated and a chromatogram is obtained. The paper is sprayedwith resorcinol solution.

(i) A common use of ethanol is in alcoholic drinks. In this experiment it is used as asolvent. Give one other use.

.. .[1]

(ii) Why is the datum line drawn in pencil?

.[1]

(iii) Suggest a reason why it is necessary to spray the chromatogram with resorcinol.

..............

.. [2]

(iv) Describe how chromatography could be used to show that the hydrolysis of starchproduces only one sugar, glucose.

...................................................................................................................................